function [a,cov_1db] = lpcvd_1DSurface_autocorrlength(cov,dx)
% Assume that dx is either symetric relative to 0 or dx is from 0 to a
% positive number
%
index_0 = find(dx==0);
cov_dx0 = cov(index_0);
for i = index_0:length(dx)
    if cov(i)<exp(-1)*cov_dx0;
        a = dx(i);
        cov_1db = cov(i);
        break;
    end
end
